There is little doubt that the majority of wines significantly benefit from malolactic fermentation, through a reduction in acidity and the development of subtle flavors that contribute to the complexity of sensory quality. Moreover, the vast majority of wine makers will not bottle their wines, particularly their red wines, until malolactic fermentation has been completed, because subsequent fermentation in the bottle, which can occur naturally, destroys the taste of the wine.
The traditional method of malolactic fermentation, which is still used commercially even today, is to rely on naturally occurring malolactic fermentation, as a consequence of the growth of lactic acid bacteria, such as Leuconostoc oenos, indigenous in the wine. The malolactic fermentation converts the malic acid in the wine to lactic acid which reduces the acidity and adds a softer flavor to the wine. However such fermentation is unpredictable as if and when it occurs after the initial fermentation. There has been a strong move by wine makers to induce malolactic fermentation by adding cultures of lactic acid bacteria such as Leuconostoc oenos, although not limited to such. Thus other lactic acid bacteria including other forms of the lactobacillus, pediococus and leuconostoc bacteria have also been used.
One method employed to initiate controlled malolactic fermentation is to add a small proportion of another wine that is already undergoing the fermentation and thus contains a high number of malolactically active bacteria. The bacteria in the added wine are adapted to wine conditions and will usually be capable of initiating or completing the malolactic fermentation in the seeded wine. An easier way to initiate malolactic fermentation is to use freeze-dried or frozen starter cultures of lactic acid bacteria, which are commercially available. The freeze-dried or frozen starter cultures should be adapted for the fermentation before adding the bacteria to the wines to undergo malolactic fermentation. Typically the adaptation process comprises an initial thawing and/or rehydration process, the latter comprising dissolving the freeze dried composition in water and adding various nutrients such as sugar, vitamins, minerals or yeast extract and keeping the resulting solution at room temperature for at least sixty minutes. The rehydrated or thawed bacteria are then normally subjected to an activation step normally lasting from three to four days in a medium which generally comprises grape juice or dilute wine to which yeast extract has been added. The resulting activated lactic acid bacteria are then added to wine subsequent to the alcoholic fermentation to initiate and/or complete the malolactic fermentation. Other methods of activating are known in the art and can be similarly employed in the present invention.
The addition of the concentrates of the malolactic active bacteria, even when added in sufficient concentration is frequently subject to a slow and nonuniform conversion of the malic to lactic acid. Agitation is not seen as being beneficial and can adversely affect the quality of the resulting wine. Such slow conversion may also be the result of the high acidity of the wine to be converted. It is desirable to achieve rapid and uniform conversion of the malic acid with bacteria concentrates specifically developed for malolactic fermentation in that competing growth of indigenous lactic acid bacteria adds undesirable flavors to the wine and should be minimized. It is further desirable to be able to conduct the malolactic fermentation with higher acidity wines that would otherwise inhibit or slow the conversion of the malolactic fermentation.